(1) Field of the Invention
The present invention relates generally to an apparatus and method for self diagnosing an integrated microcomputer system having an architecture of a plurality of engine component operation controlling systems applicable to an internal combustion engine to determine a presence or absence of failure in any one or each of the controlling systems.
(2) Description of the Background Art
In the internal combustion engine of an automotive vehicle, a failure in an exhaust gas recirculation (EGR) system, deterioration in a catalytic converter, and/or failure in an evaporated fuel processing system using a canister are self diagnosed by their integrated control unit. When any one or some of the failures is detected, a previously proposed self-diagnosing apparatus uses an alarm unit on an instrument panel to warn of occurrence of the failure in the corresponding engine component controlling system using a memory in a remote control unit.
As another example, a Japanese Patent Application First Publication No. Showa 62-51746 published on Mar. 6, 1987 exemplifies another failure diagnosing apparatus for the exhaust gas recirculation system of the engine. In the disclosed failure diagnosing apparatus, an exhaust gas recirculation control valve of the EGR system is forcefully opened and closed when the engine falls in a predetermined operating region. A change in intake air pressure in an engine intake air passage is monitored to diagnose an operation of the exhaust recirculation system.
A Japanese Patent Application First Publication No. Showa 63-205441 published on Aug. 24, 1988 exemplifies another previously proposed self-diagnosing system in which air-fuel mixture ratio sensors or 0.sub.2 sensors are disposed in an exhaust passage of upstream or downstream sides of the catalytic converter. With both output signals derived and monitored from the 0.sub.2 sensors, the deterioration of the catalytic converter is diagnosed.
A Japanese Patent Application Second Publication No. Showa 58-11067 published on Mar. 12, 1981 exemplifies a previously proposed evaporated fuel processing having a canister which prevents flow out of the vaporized fuel generated in a fuel tank toward the external. The field of the evaporated fuel processing system demands such a self diagnosing system as described above, the self diagnosing system carries out the diagnosis such that a temperature change and air-fuel mixture ratio change are monitored after the start of discharge of, e.g., purge gas.
Although it is necessary to execute various types of self-diagnosis under particular engine operating conditions, various diagnostic conditions, in other words, engine loads and engine revolution speeds required to start respective diagnostic operations are often overlapped according to contents of the self-diagnosis,
Hence, while any one of the self diagnosis is being executed, a diagnosis condition for the self-diagnose is simultaneously established.
In this case, If the self diagnosis currently being executed is continued without stop and with a high priority and the other self diagnosis whose diagnostic condition is thereafter established is not currently executed, the substantive self diagnosis for the exhaust gas recirculation system whose diagnostic condition is relatively difficult to be established could not be executed any more.
Conversely, If the self diagnostic currently being executed is suspended and the other self diagnosis whose diagnostic condition is thereafter established is started, an effective frequency of the self diagnostic operations is remarkably reduced since it is necessary to sufficiently adsorb an evaporated fuel component onto the canister in the case of the self diagnosis for the evaporated fuel processing system.